1. Field of the Invention
The present invention relates to a technique for reducing the size and cost of a discharge lamp device for a vehicle. The device is configured to turn on and control a plurality of discharge lamps with a lighting circuit.
2. Background of the Invention
A known lighting circuit for a discharge lamp (such as a metal halide lamp) as a light source for a vehicle includes a DC power circuit, a DC-AC converting circuit and a starting circuit (a so-called starter circuit).
When a plurality of discharge lamps is used as a light source, they need to be controlled. If the lighting circuit for control is provided for each discharge lamp, a problem of cost and space becomes a factor.
For example, when separate discharge lamps (a so-called four-lamp illumination) for a vehicle serve as a main beam (high beam) and a dipped beam (low beam) respectively, a pair of discharge lamps is required for each side of the vehicle and a lighting circuit is required for each pair of discharge lamps. A rated power is supplied to the discharge lamps after the lamps are turned on and reach a steady lighting state so that constant power can be controlled.
In a conventional device, a rated power of the discharge lamp is supplied to a discharge lamp for main beam and a discharge lamp for dipped beam when they are turned on and in steady-state. Consequently, a load on the lighting circuit becomes a factor of consideration.
In other words, if the sum of the value of the power supplied to the discharge lamp is large, a power loss calculated based on the efficiency of the lighting circuit is increased. Therefore, a circuit component may encounter heat and failure problems. In terms of durability, circuit components would have to have higher breakdown voltage and current values. Such components lead to increased costs and size of a circuit.
An object of the present invention is to reduce the size and cost of a discharge lamp device for a vehicle, which can turn on both a discharge lamp for main beam and a discharge lamp for dipped beam.
An implementation of the present invention provides a discharge lamp device for a vehicle comprising a discharge lamp for main beam, a discharge lamp for dipped beam and a lighting circuit capable of controlling lighting of the discharge lamps at the same time, wherein a power supply is controlled such that a sum of a value of power supplied to each of the discharge lamps is smaller than that of a rated power value of the discharge lamp in a steady-state condition in which the discharge lamps are on.
According to an implementation of the present invention, the sum of the supplied power values under steady lighting state of each discharge lamp is smaller than that of the rated power value of the discharge lamp. Consequently, it is not necessary to use components having a high breakdown voltage value for the lightning circuit as those in the conventional device.